1. Field of the Invention
The field of the invention is wheeled land vehicles having frames and running gear, such as motorcycles, and also having a movable rear wheel having the upward and downward motion controlled by an adjustable hydraulic suspension unit such as a shock absorber. Also adjustable hydraulic units such as shock absorbers having multiple chambers and adjustable preset pressure provided by an air valve.
2. Description of the Prior Art
Prior art includes compound shock absorbers utilizing an exterior gas supply for adjustment in the manner shown in U.S. Pat. Nos. 3,909,035; 3,897,940 and 4,132,395 but the arrangement and function is different from that shown in the present invention. Also, it is quite common to locate such shock absorbers on the rear wheel of a motorcycle interposed with the frame, such as shown in U.S. Pat. Nos. 4,022,484 and 4,076,271, although the location of the shock absorber in those patents is not the same as in the present invention and the operation is different. The shock absorbers used on motorcycles and particularly dirt bikes are inefficient for a number of reasons. First, the shock absorbers are not adequately adjustable so as to accommodate different size and weight of riders as well as that rider's preference for the ride desired for the type of terrain. Secondly, many dirt bike shock absorbers fail because of the repeated use over a course building up heat and agitating the hydraulic fluid in such a manner as to create inefficiency of operation. Thirdly, conventional dirt bike shock absorbers do not provide a proper adjustment for the dampening effect with some sort of valve means that can be set by the rider. The present invention overcomes these disadvantages through the use of several adjustments including four separate valve adjustments, which may be optionally selected for the manufacture of a unit, permitting operations and settings for conditions which severely increase the compressive loading on the unit, such as upon landing from a jump or hitting an obstruction, adjustment for conditions which moderately increase the compressive load on the unit, setting for equilibrium conditions and adjustment and operation for full extension of the unit.